Calcium Oxalate stones are the most common type of kidney stone. Roughly 70% of people who form kidney stones form calcium oxalate stones. Calcium oxalate crystals form when calcium combines with oxalic acid. Calcium Oxalate stones can form for many reasons. Some are results of systemic disease such as bowel disease, primary Hyperparathyroidism, or primary hyperoxaluria. Outside of systemic disease, most people form calcium oxalate stones due to diet, inheritance, and from other aspects of daily living.